First of all, make sure your cats aren't from the same ELF, or you may inbreed.
Butterfly feeders are simple to make and really seem to work under ideal conditions. A simple bowl of sugar water or Hummingbird nectar with a plastic kitchen scrubber in the middle is all it takes to feed your butterflies. Bright colors help attract them to their food source as well, so get a brightly colored scrubber. It should be submerged with the last 1/2 " above the solution. Place in a well lit area of the enclosure. Change daily and augment with a potted flower or fresh cut flowers.